Landsat TM Radiation Calibration and atmospheric correction steps

Procedures for calibration and atmospheric transfer from http://emuch.net/html/201107/2764559.html Landsat TM

I. Prepare to download raw TM data from USGS or the University of Maryland,
The data downloaded from the USGS website is raw data, in the ENVI software file-open external file-Landsat-geotiff with Meta, you only need to open ************ _mtl.txt to open all band data (except band6)
The data downloaded from the u. Maryland University website may not be the original data, in the ENVI software file-open external file-Landsat-geotiff with Meta, you only need to open ***********. met to open all band data (except band6)

Ii. Radiation Calibration

1. As ENVI 4.7 has a dedicated radiation calibration module. After opening the original TM image, select
Basic tools-preprocessing-calibration utilities-Landsat Calibration

2. Go to the next step and select Landsat 4, 5, or 7 Based on the sensor type. Obtain the data acquisition time, sun elevation, from the header file of the remote sensing image. If you use the file-open external file-Landsat-geotiff with Meta (FAST) method, sun elevation is complete. Here, pay attention to the choice of calibration type as radiance. Output file. The calibration is complete.

Iii. Atmospheric correction

The ENVI flaash module can be used for simple atmospheric correction. The following are the steps for the flaash operation:
1. The flaash module can be accessed through spectral-flaash or basic tools-preprocessing-calibration utilities-flaash.

2. The operation interface of the flaash module is divided into three parts: the upper part sets the input and output files, the middle part sets the sensor parameters, and the lower part sets the atmospheric parameters.

3. Set the input and output files first. The flaash module requires the input of the spoke brightness image and the output of the reflectivity image. Previously, we performed radiation calibration to obtain the spoke brightness image. Here we want to convert the bsq format image to the BIL or BIP Format Image, then select the converted image from input radiance image. (Basic tools-convert data (bsq, bil, BIP )). Note that after the image is input, the program will let you choose the scale factor, that is, the ratio between the original spoke brightness unit and the ENVI default spoke brightness unit. ENVI's default spoke brightness unit is μW/cm2? Sr? Nm, and the Unit for radiation calibration is W/m2.
? Sr? μ m, the conversion ratio between the two is 10, so select single scale factor in, fill in 10.000.

4. If the header file of the TM client does not contain any field information, you need to upload a. txt file here to include this information. A txt file contains information about the center wavelength of each TM band. If we open geotiff with Meta, we do not need to fill in band information.

5. Set the file name and location of the output file in output reflectance file and output directory for flaash files.

6. set sensor parameters. The first is the scene center location, that is, the coordinates of the remote sensing image center, and flight date, flight time GMT, which can be found in the TM header file and filled in.

7. Select Landsat TM5 from the sensor type menu. In this case, the sensor altitude is automatically filled with 705 km. The pixel size is 30 mb.

8. Enter the ground elevation field based on the actual situation of the remote sensing image study area. For example, the Hohhot City is 1.05 km.

9. The most important part is the atmospheric parameters:
A) Atmospheric Model (atmospheric mode): sub-arctic winter (SAW), mid-latitude winter (mlw), U. s. standard (US), sub-Arctic summer (SAS), mid-latitude summer (MLS), and tropical (t ). The atmospheric mode of the study area can be selected based on the longitude and latitude and time. See ENVI help.
B) aerosol model (aerosol model): There are four options: rural, urban, maritime and tropospheric. Select as needed. For an explanation of the four modes, see ENVI help.
C) When TM is selected, the optional parameters include aerosol retrieval and initial visibility. These two parameters are very important to the final results, so it is best to investigate the local initial visibility. In addition, AERONET has sites around the world for the determination of AOD (atmospheric optical depth). You can query the sites after Aod is converted to the extinction coefficient, and estimate the visibility by the extinction coefficient. This step is cumbersome, we will not detail it here. If the visibility is calculated using the K-T Algorithm in aerosol retrieval and the result can be calculated, the K-T
Algorithm visibility, no
The visibility specified by initial visibility is used.
D) about aerosol retrieval. If you select the K-T method from the drop-down menu, you need to set the parameter in the multispectral settings, select over-land retrieval standard (660: 2100nm) in assign default values based on retrieval conditions. Different models can be set based on different study areas. Other settings can be left unchanged. Apply.
Note: sort the information on the Internet. From http://emuch.net/html/201107/2764559.html